The present application is a continuation of International Application No. PCT/SE2005/000179, filed Feb. 9, 2005, which claims priority to SE 0400453-7, filed Aug. 23, 2004, both of which are incorporated by reference.
The present invention relates to an exhaust valve mechanism for an internal combustion engine with at least one exhaust valve in each engine cylinder, which mechanism comprises a main rocker arm for each cylinder mounted on the rocker arm shaft for normal operation of the exhaust valve by the actuation of a camshaft with a cam element for each rocker arm and a secondary rocker arm arranged on the main rocker arm and mounted on a rocker arm shaft, for the activation of an exhaust brake function, which activation is achieved through the supply of hydraulic pressure to a piston cylinder which acts between both the rocker arms and takes place through the effect of one of the cam elements of the camshaft.
A valve mechanism in accordance with the foregoing is previously disclosed through WO 03/031778, for example, which can be utilized in conjunction with a special type of camshaft with exhaust cams with extra lobes to increase the braking effect of the engine. For example, it is possible to use a higher valve lift height, which gives a more effective gas exchange in the cylinder under engine braking. Such a valve mechanism can also take up greater forces, which means that a higher differential pressure can be permitted over the exhaust valve, which permits a significant increase in the braking effect.
When the exhaust valves in this previously disclosed valve mechanism are to open for the main lift (normal engine function), this is only performed via the main rocker arm. During this sequence, the secondary rocker arm can adopt any desired position between two outer end positions, where it is able in one extreme position to bear against its cam element, and in the other extreme position to accompany the main rocker arm. This angular interval, which is circa 10°, can cause undesired wear or damage to the valve mechanism, when the secondary rocker arm bears against either its cam element or the main rocker arm. Another problem is that the secondary rocker arm is subjected to unilateral loading under active engine braking, which reduces the thickness of the oil film at its bearing point, which can also lead to wear.
It is desirable to bring about an improvement in a valve mechanism of the kind indicated in the introduction, so that the above-mentioned problems can be avoided.
This is achieved in accordance with the invention in that a spring device is so arranged as to act between a fixed point on the engine and the secondary rocker arm, in such a way that the latter rocker arm is caused by the spring force to engage with the cam element of the camshaft.
Undesired movement in the secondary rocker arm during normal engine function is avoided by means of the invention. It is also possible to increase the oil film thickness at the bearing point of the secondary rocker arm by simple means.